Footprints of speciation and hybridization in the genomes of Galápagos iguanas

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Volcanic islands can be seen as “natural laboratories” of evolution as many important evolutionary processes can be observed and reconstructed under simpler conditions compared to mainland settings. One of the major evolutionary processes that take place on such islands, is the arrival and subsequent evolution of species on islands usually represented by a limited number of founder individuals. Following arrival, species have to adapt to new environmental conditions often resulting into the evolution of new species and sometimes entire adaptive radiations of species. The Galápagos archipelago is probably the most famous setting of purely oceanic volcanic islands with endemic species, some of which became textbook examples of evolutionary biology. Having arrived more than 10 million years ago on the archipelago, a lineage of South-American lizards diversified on the Galápagos archipelago into land (genus Conolophus) and marine iguanas (genus Amblyrhynchus). Like no other lizard worldwide, marine iguanas have fully adapted to the marine environment. Moreover, the various island populations of marine iguanas provide a unique system to study the effects of two major evolutionary forces – local adaptation/speciation versus hybridization. By sequencing the genomes of Galápagos iguanas and their sister taxa from the South-American mainland (species of the genera Cachryx and Ctenosaura), we will unravel genomic signatures of the divergence of Galápagos iguanas and the subsequent differentiation of land and marine iguanas, respectively. This will allow us to identify genomic regions (genes) that are in general under selection when species face new environmental conditions on islands and more specific, genes that underlie the unique adaptation of a lizard species to the marine environment. Based on the full reference genomes of marine and land iguanas, we will further test our hypothesis that local adaptation and hybridization result into the integration of the genomic equivalents of adaptations on a local level into a common species gene pool of the marine iguana by recurrent hybridization events. Such a process would enhance the evolutionary potential of a species. We will follow up our hypothesis by first conducting a local field study, which provides a current insight on the processes of local adaptation and hybridization on the island of San Cristóbal. Second, by integrating the insights from this snapshot into a broader evolutionary framework, we will analyse the consequences of both effects on a population genomics as well as transcriptomic/proteomic level. To do so, we will include island populations of the marine iguana represented by low coverage genomes and transcriptomic profiles. Observed genomic patterns will be compared with patterns found for the system of the Galápagos land iguanas, in which phylogenetic divergence (speciation) without hybridization is evident on an evolutionary time scale.